This application relates generally to optically active fluorinated vasoconstrictors, methods and reversibly soluble enzymes employed for making them, and anesthetic formulations comprising them. One typical use for a vasoconstrictor is as an ingredient of a local anesthetic composition.
Typical local anesthetic injections are composed of the following ingredients:                Lidocaine hydrochloride (anesthetic, FIG. 1)        (R)-(−)-Epinephrine bitartrate (vasoconstrictor, FIG. 2. The vasoconstrictor impedes systemic absorption, increases duration of anesthesia, and allows rate of drug metabolism to equal rate of drug absorption.)        Sodium or potassium metabisulfite (antioxidant)        Sodium chloride to achieve isotonicity        EDTA or citric acid (chelating agents)        Water (solvent; pH is adjusted to 3.3-5.5 with HCl or NaOH)        Minor impurities such as aluminum salts        
Local anesthetics employed for dental and medical applications are ubiquitous pharmaceuticals in the private sector and military. Jastak, J. T.; Yagiela, J. A. J. Am. Dent. Assoc. 1983, 107, 623-630. Current formulations work well in hospitals, but quickly lose their efficacy during transport and storage in field austere environments where climate control may not be available. Hondrum, S. O.; Seng, G. E.; Rebert, N. W. Anesthesia and Pain Control in Dentistry 1993, 2, 198-202. Madden, J. F.; O'Connor, R. E.; Evens, J. Prehospital Emergency Care 1999, 3, 27-30. Thus, it is important to develop new thermo- and photo-stable local anesthetic formulations. Although lidocaine is relatively stable to harsh environmental conditions, previous investigations suggest a correlation between the loss of efficacy of anesthetic injections and decomposition of the contained vasoconstrictor. Hondrum, S. O.; Seng, G. E.; Rebert, N. W. Anesthesia and Pain Control in Dentistry 1993, 2, 198-202. Madden, J. F.; O'Connor, R. E.; Evens, J. Prehospital Emergency Care 1999, 3, 27-30.
New vasoconstrictors should adhere to four main criteria:                1) Resist acid-catalyzed racemization        2) Experience little or no photochemical destruction        3) Exhibit α-adrenergic properties similar to epinephrine, with minimal β-adrenergic activity        4) Retard the rate of systemic absorption of the anestheticMechanism of Racemization of Aminophenylethanols        
Evidence suggests that a major pathway for destruction of 2-methylamino-1R-hydroxy-phenylethanols is racemization. While the role of light in this process is not fully understood, the key step of acid-catalyzed elimination of the OH-group at the chiral center is without doubt (Table 1 and FIG. 3). Venter, D. P. Tetrahedron 1991, 47, 5019-5024. From the data in Table 1, it is clear that p-hydroxy aminophenylethanols racemize markedly faster than compounds possessing p-methoxy-groups, and those without p-substituents are practically unreactive toward racemization in acid media. The simplest plausible mechanism to explain this data would involve a loss of the hydroxyl group at the chiral center, resulting in the formation of unstable achiral quinone intermediates. In the reverse reaction, these intermediates can form both stereoisomers at the same rates, resulting in racemization.
TABLE 1Racemization of substitutedaminophenylethanols in 1.0 M HCl at 30° C.[1.]CompoundRate constant, (min−1)R1 = H, R2 = OH, R3 = CH33.2 10−7R1 = R2 = H, R3 = CH(CH3)8.4 10−7R1 = R2 = OCH3, R3 = CH(CH3)1.0 10−4R1 = OCH3, R2 = H, R3 = CH(CH3)1.5 10−4R1 = R2 = OH, R3 = CH34.1 10−4R1 = R2 = OH, R3 = CH(CH3)24.5 10−4[1.]Venter, D. P. Tetrahedron 1991, 47, 5019-5024. 
J. R. Ammann and colleagues applied this idea to the interpretation of their studies of the stability of commercial anesthetic injections. Canca{overscore (n)}ón, F.; Paulus, B. F.; Thompson, g. A.; Ammann, J. R. Investigation of Vasoconstrictor Degradation in Local Anesthetic Injections 30th Annual Meeting & Exhibition of the AADR and 25th Annual Meeting of the CADR, Chicago, 2001. Commercial injections contain (R)-epinephrine as a vasoconstrictor, along with such additives as metabisulfite and aluminum salts. These injections also are less acidic, thus the methylamino group of the vasoconstrictor remains unprotonated. FIG. 4 depicts the proposed mechanism of racemization of epinephrine through interactions with the additives in commercial anesthetic injections.
Requirements 3 and 4 (see above) impose severe limitations on the “allowed” structure variations of the epinephrine molecule. (R)-Epinephrine binding to α-adrenergic receptors is very effective, having a binding constant with respect to α1-receptors on the order of 1 μM and to α2-receptors on the order of 0.01 μM. Lu, S.; Herbert, B.; Haufe, G.; Laue, K. W.; Padgett, W. L.; Oshunleti, O.; Daly, J. W.; Kirk, K. L. J. Med. Chem. 2000, 43, 1611-1619. Binding of (R)-phenylephrine with α-receptors is also characterized by binding constants on the order of several μM. Kirk, K. L.; Olubajo, O.; Buchhold, K.; Lewandowski, G. A.; Gusowski, F.; McCulloh, D.; Daly, J. W.; Creveling, C. R. J. Med. Chem. 1986, 29, 1982-1988. Therefore, (R)-epinephrine and (R)-phenylephrine molecules fit precisely in the binding cavity of the receptors, and any substituents that significantly change the size of the molecule likely will disturb binding.